The invention generally relates to a rubber bearings and, more particularly, to an improved hydraulically damped rubber bearing.
German Utility-Model Patent 76 16 276 discloses a rubber bearing having a liquid-filled working chamber in which first means are provided for damping low-frequency vibrations below 20 Hz and second means are provided for damping high-frequency vibrations above 20 Hz. The first means is formed by an elastically expandable bearing spring defining the working chamber and having a first expanding compliance and by a damping opening, through which fluid is displaced to dissipate energy when low-frequency vibrations are introduced. The second means is formed by a conduit, which connects the working chamber with a surge chamber and has a funnel-shaped crosssection in the direction of the working chamber. This conduit is closed off opposite the surge chamber by a damping element having a resistance to flow R. At its narrowest location, the conduit has the characteristic wave impedance Zw.
The first means used to damp low-frequency vibrations thereby comprises a damping opening having a duct-type design. When low-frequency vibrations are introduced, the liquid volume contained in this opening attains a resonant movement to effectively damp the vibrations. When high-frequency vibrations are introduced, the resonant movement of the contained liquid is brought to a standstill and the second means becomes active. The second means comprises an elastically supported membrane, which serves to insulate pressure changes in the working chamber caused by the introduction of the high-frequency vibrations. Because the membrane is flexibly supported, however, the insulation achieved is not very good. In any case, residual forces remain, which are transmitted via the rubber bearing. This becomes clearly evident when low-frequency vibrations are introduced at the same time as the high-frequency vibrations. In these instances, the membrane temporarily makes contact against the inflexible end stops of the rubber bearing. At this point, the membrane is completely ineffective as the high-frequency vibrations are transmitted in an unmitigated state.